Canon EOS Rebel T7i/800D For Dummies
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Everything in space is moving and turning. Objects can't sit still. Thanks to gravity, other celestial bodies are always pulling on a star, planet, galaxy, or spacecraft. Some of us are self-centered, but the universe has no center.

For example, Earth

  • Turns on its axis — what astronomers call rotating — and takes one day to turn all the way around.
  • Orbits around the Sun — what astronomers call revolving — with one complete orbit taking one year.
  • Travels with the Sun in a huge orbit around the center of the Milky Way. The trip takes about 250 million years to complete once, and the duration of the trip is called the galactic year.
  • Moves with the Milky Way in a trajectory around the center of the Local Group of Galaxies, a couple of dozen galaxies in our neck of the universe.
  • Moves through the universe with the Local Group as part of the Hubble Flow, the general expansion of space caused by the Big Bang.

    The Big Bang is the event that gave rise to the universe and set space itself expanding at a furious rate. Detailed theories about the Big Bang explain many observed phenomena and have successfully predicted some that hadn't been observed before the theories were circulated.

Remember Ginger Rogers? She did everything Fred Astaire did when they danced in the movies, and she did it all backward. Like Ginger and Fred, the Moon follows all the motions of Earth (although not backward), except for Earth's rotation; the Moon rotates more slowly, about once a month. And it performs its tasks while also revolving around Earth (which it does about once a month).

And you, as a person on Earth, participate in the motions of rotation, revolution, galactic orbiting, Local Group cruising, and cosmic expansion. You do all that while you drive to work, whether you know it or not. Ask your boss for a little consideration the next time you run a few minutes late.

About This Article

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About the book author:

Julie Adair King is a veteran digital photography author and educator whose books are industry bestsellers. Along with Digital Photography For Dummies, she is the author of bestselling guides to many Canon dSLR cameras. Her books have sold more than a million copies.

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